This invention relates to a gas turbine with several shroud segments which enclose rotor blades of a turbine wheel as a seal, with the shroud segments having at least a front or a rear attachment at the radially outward area of stator vane segments, and with each of the stator vane segments being located at their inner area on a control ring.
Such a design is disclosed in Patent Specification GB 2 061 396 A.
The control ring, by way of its thermal expansion, is used to adjust the outer circumference of the stator vane segments to the respective thermal conditions. Thus, the overall diameter of the ring formed by the shroud segments is decreased or increased, dependent upon temperature. In this manner, adjustment of the gap between the tips of the rotor blades and inner area of the shroud segments is achieved. Without such adjustment, thermal contraction or expansion of the rotor blades would lead to an increase of the gap or to a contact with the shroud segments.
Accordingly, the idea underlying the state of the art is to achieve optimum passive running gap control. As described, this is achieved by a thermal operating behavior of the attaching means of the shroud segments that is synchronized with the radial movement of the tips of the rotor blades. Ideally, the running gap in steady-state operation will not be affected by non-stationary operating conditions.
The known designs are disadvantageous in that optimum running gap control cannot be achieved under all installation conditions, this being due to the fact that the installation dimensions of the control ring, the stator vane segments and the shroud segments are invariable.